The cycle begins with the beginning of valley development, and at that stage drainage is in its _infancy_. The type of the infant valley is the gully or ravine (Figs. 67 and 68). It has steep slopes and a narrow bottom. Fig. 1 of Plate IV represents similar, or rather older, ravines in contour (shore of Lake Michigan, just north of Chicago). With age, the valley widens, lengthens, and deepens, and passes from infancy to _youth_. In this stage also the valleys are relatively narrow, and the divides between them broad. They may be deep or shallow, according to the height of the land in which they are cut, and the fall of the water flowing through them; but in any case the streams flowing through them have done but a small part of the work they are to do before the country they drain is base-leveled. Figs. 69 and 70, respectively, represent youthful valleys in regions of moderate and great relief. Fig. 2, Plate IV, shows a youthful valley in a region of slight relief (near Casselton, N. D., lat. 46° 40′, long. 97° 25′). The uppermost line in Fig. 64 likewise represents topographic youth, as shown in cross-profile. [Illustration: +Fig.+ 68.—A gully somewhat older than that shown in Fig. 67. (Alden.)] [Illustration: +Fig.+ 69.—A young valley in a region of slight relief.] Not only are narrow valleys said to be young, but the territory affected by them is said to be in its topographic youth, since but a small part of the time necessary to reduce it to base-level has elapsed. An area is in its topographic youth when considerable portions of it are still unaffected by valleys. Thus the areas (as a whole), as well as the valleys, represented on Plate IV, are in their topographic youth. It is often convenient to recognize various sub-stages, such as early, middle, and late, within the youthful stage of valleys or topographies. The different parts of the areas shown on Plate IV, for example, represent different stages of youth. Youthful streams, as well as youthful topographies, have their distinctive characteristics. They are usually swift; their cutting is mainly at the bottom rather than at the sides, and their courses are often marked by rapids and falls.